Autodesk Robot Structural Analysis

[#1]

Hello,

I have generated 3D frame using RSA 2013 professional. When i verify the rafter beams under ultimate limit state, the results shown are instable. And when optimized under ULTIMATE it provides very large dimension beams. whereas when i used SERVICEABILITY METHOD, it is fine. 

Please help me, how to verify beams in 3D generator. 

Please find attached 3D design file

Kind regards,

Ajmal

[#2]

I ain't able to attach rsa file, please help me

find result snaps for reference

why can't i design beam under ULS 

[#3]

ULS and SLS check are two different verifications,. As far as I can see the problem you have got is the exceeded slenderness limit. Looking at the buckling Z part you can see that unrestrained buckling length for 140 section is over 14m which way  too long weak the axes if this section. Have you set the buckling parameters correctly?

[#4]

I haven't set the paramters. I am a learner, student. how to set, will you please help me

Thanks

Ajmal

[#5]

The beam length is 7.11 m

bay width is 14 m

[#6 · Accepted solution]

Assuming it is a 2 span beam then either you set buckling Z (and LTB) coefficients as 0.5L or you should define an intermediate restrain at this point and then set these coefficients as 1.0L  for each of the spans.

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